Petrological study of spinel peridotites of Nidar ophiolite, Ladakh Himalaya, India

摘要

Petrological study of the ultramafic rocks from the Nidar Ophiolite Complex (NOC) of the Indus Suture Zone is carried out. The study of Cr-spinels along with olivine and pyroxenes emphasizes the genesis and tectonic setting of the ultramafites. Olivine from the harzburgite is Mg-rich, with the molar ratio Mg# [$m{Mg/(Mg + Fe^{2+}}$)] varying between 0.91 and 0.94 and olivine in dunite between 0.92 and 0.94. Clinopyroxene from the harzburgite is $m{TiO_{2}}$ and $m{Na_{2}O}$-poor diopside ($m{Wo_{47a??50}En_{47a??50}Fs_{2a??4}}$). Spinel in harzburgite shows wide Cr#, molar ratio varied between 0.26 and 0.72, and significantly higher in dunites with Cr# ranges from 0.69a??0.85. Cr# of the peridotite spinel follow a depletion trend. Calculated equilibrium conditions of the samples are $800a??900^{0}m{C}$ temperature, 32 and 40 kbar pressure, oxygen fugacity -0.09 to 0.55 log units above the FMQ buAer. Residual nature of the harzburgites and the presence of high and low Cr# spinels may be due to the genetic artifact of the different ultramafic units.